The present disclosure relates to pressure sensors and systems comprising such sensors. In particular, the present disclosure is directed towards sensors and sensor systems that may be used for measuring pressure on a body part.
Hence, the present disclosure relates to particles that may form part of sensor elements, sensor systems, clusters of sensor elements and devices for measuring pressure on a body part.
There are many applications in which it may be desirable to measure pressure on a body part. As a non-limiting example, it may be desirable to measure pressure on a body part in connection with compression treatment of the body part. Compression therapies may be used for treatment and/or prophylaxis of a number of conditions, including, but not limited to, Deep Vein Thrombosis (DVT), vascular disorders, circulatory disorders, edemas, heart conditions (treated by counterpulsation), lymphedema, burns, injuries, and embolisms.
Some devices for compression treatment are known in the art, e.g., from US 2004/0073146 AI, US 2004/0073146 AI, US 2002/0173735 AI, U.S. Pat. No. 6,494,852 B1, U.S. Pat. No. 5,997,465, U.S. Pat. No. 6,123,681, U.S. Pat. No. 6,198,204 B1, EP 1 324 403 AI, US 2004/0167375 AI, WO 2004/093763 AI and US 2005/0043657 AI.
Presently available systems for measuring pressure on a body part, however, suffer from a number of drawbacks. Major issues with existing measurement systems have been identified in the areas of mismatched mechanical properties (body/device impedance mismatches and resulting interface stress modification), sensitivity (often too high), quiescent impedance (often nearly infinite), nonlinearity, poor repeatability (cycle to cycle and insertion to insertion), creep, hysteresis, and sensitivity to curvature, temperature-pressure-humidity, etc.
Generally existing sensors have excellent precision (which is good) and perform well at high pressures in planar, mechanically isolated spaces between well characterized surfaces. Such spaces and surfaces are not available in the case of devices for measuring pressure on a body part.
U.S. Pat. No. 2,951,817 discloses a variable resistance material, comprising a body of elastomeric polyvinyl chloride with a granular filler selected from a group consisting of precipitated manganese dioxide and microphone carbon granules.
U.S. Pat. No. 3,629,774 discloses a progressively collapsible variable resistance element, comprising an elastic cellular structure of, e.g., elastomer foam. Examples given include silicone rubber, natural rubber, latex and polyurethane rubber. The element further comprises a conducting coating provided on the inside of the cells in the structure. Examples of coating materials are carbon (graphitized, partially graphitized, carbon black), silver, gold, copper, tungsten, aluminum, and other metals.
U.S. Pat. No. 4,292,261 discloses a pressure sensitive conductor and method of manufacturing the same. The conductor comprises an isolating elastomer having electrically conductive magnetic particles dispersed therein.
U.S. Pat. No. 6,388,556 B1 discloses a film pressure sensitive resistor and pressure sensitive sensor. The film comprises a binder, spherical elastomeric particles and conductive particles, such as carbon black. Examples of conductive particles comprise graphite, carbon black, indium-doped tin oxide and the like. Examples of elastic organic fillers comprise silicone polymer, acrylic polymer, styrene polymer, urethane polymer and the like. Examples of spherical elastomeric particles comprise nylon particles. The binder may be a silicone rubber, polyurethane resin, epoxy resin, phenol resin or polyester resin.
U.S. Pat. No. 6,291,568 B1 discloses a polymer composition comprising an electrically conductive filler material selected from a group consisting of powder-form metallic elements and alloys, electrically conductive oxides of such elements or alloys and mixtures thereof, mixed with a non-conductive elastomer.
The above described sensors are of a conductive elastomer type, and constitute composites of an elastomeric matrix and a conductive particle filler. When such composites are used in practice, strain related damage occurs easily, and as such, creep, hysteresis, and electrical aging are all increased significantly. At such high loading levels so as to induce finite quiescent impedance, the viscoelastic properties of the composite degrade dramatically and their usefulness as “pressure sensorsu is greatly diminished.
U.S. Pat. No. 6,388,556 B1 discloses, as prior art for the invention patented therein, a variable area type pressure sensor, wherein a conduction path between first and second coplanar electrodes is variable in response to a pressure applied on the sensor. It is recognized that this type of sensor does not provide a smooth resistance-load curve.
Such sensors do not provide the desired accuracy needed in measuring pressure on a body part.
Hence, there is a need for improvements in sensors for measuring pressure on a body part.